1. Field of the Invention
This invention relates to apparatus for engaging a concrete slab during hoisting of the same.
2. Description of the Prior Art
U.S. Pat. Nos. 361,927; 560,329; 880,962 and 2,563,164 disclose "Lewises" which cooperate with a dovetail shaped slot in a block of building stone to afford a grip on the stone.
U.S. Pat. No. 3,652,118 discloses a lifting anchor for concrete slabs which employs a wedge engageable with a socket cast in the concrete slab.
U.S. Pat. No. 3,590,538 discloses a threaded socket cast into a concrete slab which can be engaged by a threaded bolt.
U.S. Pat. Nos. 3,431,012; 3,596,971 and 3,705,469 disclose concrete slab engaging devices which are operated by rotation of a hoisting member relative to a socket formed in the slab.
Copending commonly assigned U.S. application Ser. No. 641,529 filed Dec. 17, 1975 discloses a socket formed in a concrete slab and a mechanism for effecting selective engagement in the socket for hoisting the slab.